Misfiring Cylinder - Burnt Spark Plug

Maintenance/Repairs
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1

I have a 4 cylinder, 2002 Nissan Altima with about 170,000 miles on it.
About 2 months ago, the car starting misfiring while driving and the engine light came on. I went to autozone, used their diagnostic tool and it said I needed to replace the fourth cylinder’s ignition coil. I ended up just replacing the spark plugs at that point. After replacing the spark plugs, the misfiring seemed to stop, but the check engine light was still on although the car ran great in comparison.

Then, about 2 weeks ago, the car started smelling like gas and slightly misfiring again. I bought set of ignition coils and changed them out. I started it up, the car seemed to work great. I went to the store about an hour later and the car worked better all the way there with no problems. Then, as I was about to leave the store, I started the car up and it started sputtering and misfiring and you could visibly see the engine shaking like crazy when I popped the hood. It stopped shaking, evened itself out, after about a minute. Then, I felt the top each of the coils and the first three were fine, but the fourth had a rapid tapping coming from it that was obviously not right.

I gave it a couple of days, but the car didn’t stop smelling like gas or misfiring when starting up, so I pulled out the ignition coils and the spark plugs.
The fourth spark plug was brown and burnt from the bottom to the halfway point, unlike the other still-clean spark plugs. My first hopeful thought was, maybe it wasn’t tight enough and that was letting gas or oil inside to burn. I tightened it up, put everything back and it seemed to be alright, even the tapping from the coil stopped.

However, within the last couple days, the car has been smelling like gas and feels like it sputters and misfires once I start it up. The misfiring seems to stop after I rev the engine a little bit, but sometimes when I’m idling, you can still smell the gas and sometimes audibly hear a sputtering.

So my question is: what the hell could be wrong? Faulty wires, a stuck valve, bad compression, what? Remember, the fourth cylinder’s spark plug was only burnt on the bottom half if that’s any help.

2

Remove the oil dip stick an smell the oil.

Does it have a gas odor?

If so, the problem might be with a fuel injector, or the fuel pressure regulator.

If it has one.

Tester

3

See what direction the fault codes point you in. Post them here and we’ll be happy to assist.
Also post photos of the plugs. There’s a lot that can be seen in their condition. There’s clues in them there plugs. Here’s a link to some charts to help determine what the clues mean.
http://www.bing.com/images/search?q=reading+spark+plug+chart&qpvt=reading+spark+plug+chart&qpvt=reading+spark+plug+chart&qpvt=reading+spark+plug+chart&FORM=IGRE

4

I’m guessing you got a P0304 (cylinder 4 misfire). They should not have told you to replace the ignition coil; there will be a list of around 4 possible causes that they should have printed for you. I know this because I work at AutoZone and do this every day at work. Frankly, this sounds more like a leaky fuel injector at that cylinder since you’ve replaced the ignition components. However, you need to verify that you actually have spark there. If the wiring to the coil is frayed and shorting out intermittently, that would also cause a misfire.

5

I was actually thinking Crank Position Sensor malfunction, perhaps intermittently telling the ECU when the #4 coil needs to be fired. However, I still recommend starting with the diagnostic codes and the plug condition. In general I prefer to start with diagnosis. Its’ usually cheaper in the long run. And I’m cheap.

Hey, NYBo, not to go off on a tangent, but have you been missing for a while? Where you been? Or is my mind skipping its tracks?

6
Hey, NYBo, not to go off on a tangent, but have you been missing for a while? Where you been? Or is my mind skipping its tracks?

Hanging out elsewhere, forum-wise. I checked in now and again. Today I discovered they made this forum a little easier to navigate (why I got frustrated and laid back in the first place), so you’ll have to put up with me again. Started my retirement job at AutoZone a few months ago so I get to brainstorm car problems and get paid for it!

Although I am trained in psychology, I can’t comment on your mind skipping its tracks. :slight_smile:

7

Welcome back. It’s good to have you with us again. Congrats on the retirement and the parts counter job. Sounds perfect.
My mind… well… it is what it is. What can I say. :smiley:

And now, back to the OP’s problem…

8

Hey, guys. Here’s a couple pictures of the fourth cylinder’s spark plug (on the right) in comparison with another plug.

9

NYBO, yeah, my next cheap step is to find out if it’s the wires themselves and possibly replace those. I need to pick up an inline spark tester soon, but I figured I might as well start posting here about it.

10
Remove the oil dip stick an smell the oil.

Does it have a gas odor?

If so, the problem might be with a fuel injector, or the fuel pressure regulator.

If it has one.

Tester

Just went out and smelled the dipstick. Yep, definitely has a faint gas smell.

11

Okay, the working ends of the plugs look reasonably similar, but the body of plug #4 is what’s off. The deposits may be allowing the power from coil to go down the outside and directly to the head rather than firing within the cylinder. Replace it and see if the misfire goes away. Any idea where the deposits came from? Is the valve cover leaking oil into the spark plug well?

12

Replace it as in purchase a new one?

13

You could try cleaning it up but if the ceramic body has been scored, it might still leak current to ground. A new one would be better.

14
Any idea where the deposits came from? Is the valve cover leaking oil into the spark plug well?

I have no clue where the deposits came from. I’m assuming it has to be fuel because of gas odor when I start the car and because, as I just recently found out, my oil dipstick smells like gas.So maybe from faulty fuel injector, but that’s one thing I’m hoping against. My last resort is taking it to a mechanic, but I may just have to do that at some point.

15

I strongly suggest a compression test. If you’re dropping a cylinder you can throw parts at it until hxxx freezes over without curing the problem.

Low compression eventually kills the spark plug which in turn kills the coil and so on.
Hopefully there is no compression issue at all but it’s a good idea to kill that possibility at the beginning.

And of course, greetings to NYBo; MIA for a while. Glad you’re back!

16

Fuel can’t reach that part of the spark plug unless it’s spraying from some sort of leak. Have you eliminated the possibility of a fuel leak?

You need to chase down the problem quickly. Gasoline makes a lousy lubricant.

17

The deposits on the one plug could be caused by the plug being loose and not fully seated. A little air and gas, perhaps partially combusted, will come out the spark plug hole on the compression stroke and coat the plug body. That would only happen though if the spark plug was not seated properly.

18
The deposits on the one plug could be caused by the plug being loose and not fully seated. A little air and gas, perhaps partially combusted, will come out the spark plug hole on the compression stroke and coat the plug body. That would only happen though if the spark plug was not seated properly.

I think you’re on to something. The washer on that plug sure make it look like it wasn’t properly seated.

19
The deposits on the one plug could be caused by the plug being loose and not fully seated. A little air and gas, perhaps partially combusted, will come out the spark plug hole on the compression stroke and coat the plug body. That would only happen though if the spark plug was not seated properly.
Actually, that was something we had been concerned with as well. However, I tightened the plug and made sure it was on well, but the misfiring and smell of gas didn't stop. I've actually removed and replaced that same one about 4 times total now.
20

If the hv connection to the spark plug has high resistance, the spark could instead travel down the surface of the plug and cause that effect too. That’s another possibility, I think was mentioned above. Iv’e had that problem on my truck, figured it out by measuring the resistance of the spark plug wires. I got a clue that might be happening b/c I noticed a slight electrical shock when touching that particular wire with the engine running. I’m not sure how to go about measuring the resistance pathways with the coil on plug design, but there must be a similar way. One more idea, there’s a small oil leak from the valve cover that just happens to be dripping on the spark plug.